Preheat broiler on high with a rack 8 inches below element.
Stir together yogurt, lime zest, 2 tablespoons lime juice, and 2 teaspoons ras el hanout; season with salt and pepper.
Season chicken; add to yogurt mixture. Let stand 20 minutes.
On a rimmed baking sheet, toss carrots with 2 tablespoons oil; season. Broil 5 minutes.
Toss chickpeas with 1 tablespoon oil and remaining 1 teaspoon ras el hanout; season. Add to sheet along with chicken.
Broil, flipping chicken once, until just cooked through and carrots are tender, 8 to 10 minutes a side.
Toss onion with remaining 2 tablespoons lime juice and 1 tablespoon oil; season.
Stir a handful of cilantro into couscous.
Serve chicken, chickpeas, and carrots over couscous with pickled onion, yogurt, more cilantro, and a drizzle of oil.
